Characteristics and Origin of Bioclastic Limestone Reservoir in Lagoon of Mishrif Formation

There are two questions need to be further clarified. The first one is what is the difference between reservoirs in lagoon and reef-shoal. Another question is how did the lagoon reservoir form. This paper mainly answers these two questions. Based on core, cast thin sections, physical property samples, SEM and CT samples, the lagoon reservoir characteristics such as the lithology, physical property, pore type and pore throat size are first analyzed. Secondly, the type of diagenesis is identified and a model of lagoon reservoir formation is established. Finally, an important and special factor is discussed. The result shows that the reservoir in lagoon are mainly packstone and wackstone with high porosity and low permeability. The pore space includes micropore, moldic pore, vuggy pore and visceral foramen. The size of pore throat is usually smaller than 5μm. Different bioclasts lay a foundation for diagenesis. The selective dissolution in marine environment and meteoric environment is the main cause for diverse secondary pores. Furthermore, bioturbation plays an important role in promoting the development of reservoirs in lagoon. Burrows developed by bioturbation could be the flow channel for diagenetic fluid, which could promote selective dissolution.